The present invention relates to a network control. system for a network. More particularly the present invention relates to a traffic control system method and therfore for an ATM network for estimating an average cell rate of data traffic and deciding admission of a connection set-up request in the network based on the estimated average cell rate.
When a user (terminal unit) requests set-up of a connection in a network being operated in an asynchronous transfer mode (ATM), the terminal unit must declare traffic characteristics of the network to the network side. In this case, it is recommended by ITU-T to use a peak cell rate as a traffic descriptor.
For service of a connection in which traffic content greatly fluctuates with time like data communication, however, it is impossible to effectively use network resources, particularly the link capacity by the above control method using only a peak cell rate as a traffic descriptor.
To solve the above problem, Japanese Patent Laid-Open No. 3-106148 discloses a control method for adding an average cell rate of data traffic in a connection requesting set-up as a traffic descriptor, calculating a bandwidth required by the connection by using a declared peak cell rate and average cell rate, and deciding whether to accept the connection in accordance with the bandwidth. This control method makes it possible to accept a new connection even if the sum of the peak cell rate of a newly declared connection and the peak cell rate of connections already accepted exceeds the bandwidth. In this case, it is proposed that the bandwidth can effectively be used by multiplexing connections statistically.
However, it is difficult to accurately estimate generated traffic characteristics depending on the type of communication service. Therefore, it is difficult to make every connection requiring set-up and declared prior to set-up and average cell rate of data traffic. For example, in the case of data communication using window control for the flow control between terminals, an average cell rate of data traffic depends on the round trip delay in a network.
This is described below by taking the network shown in FIG. 2 as an example. FIG. 2 shows an ATM network, in which numerals 1, 2, and 3 represent nodes for performing ATM switching, 4 represents a network management system, 11, 12, and 13 represent links for network management, 21, 22, and 23 represent links between nodes, 31, 32, and 33 represent subscriber links, and 101, 102, and 103 represent terminals.
In this case, it is assumed that the terminal 101 transfers a data frame to the terminal 103 through the node 1, link 23, and node 3. The terminal 101 segments the data frame into multiple fixed-length packets (ATM cells) and sends them out to the subscriber link 31. The sent-out ATM cells arrive at the destination terminal 103 through the node 1, link 23, and node 3. The destination terminal 103 reassembles the original data frame by using the received ATM cells, checks if the data frame is correctly received, and generates a response frame. The response frame is segmented into multiple cells and sent to the source terminal 101 of the data frame through the node 3, terminal 23, and node 1. The source terminal 101 reassembles a response frame by using these received cells. When reassembling of the frame ends, the terminal 101 starts transmission of the next data frame.
In this case, an average cell rate of data traffic transmitted by the terminal 101 is given as a quotient obtained by dividing the information content included in one data frame by the time (round trip delay) until the next data frame is transmitted after above data frame is transmitted. The quotient depends on the route on a connection and the delay in a node.
A terminal unit cannot know a route through which a connection requested by the terminal unit is connected to a destination unit. Therefore, if declaration of an average cell rate of transmission data is indispensable, the terminal unit cannot help assuming the worst route and also a node delay time. generated in the fluctuation range of a network load and declare the maximum average cell rate within the range in order to secure the quality of service including the cell loss ratio and cell transfer delay. Thus, problems occur that an average cell rate of data traffic actually obtained in a network is substantially less than an average cell rate declared by the terminal unit. Thus, utilization efficiency of network resources decreases substantiallly if bandwidth allocation is performed in accordance with the declared average cell rate.
It is an object of the present invention to provide a traffic control method for improving the utilization efficiency of network resources.
It is another object of the present invention to provide a network control system for decreasing the load of a user terminal when setting up a connection.
It is yet another object of the present invention to provide a traffic control method for an ATM network for estimating an average cell rate of data traffic and deciding admission of a connection set-up request in the network based on the estimated average cell rate.
To achieve the above objects, the present invention estimates an average cell rate of data traffic for a connection at the network side in accordance with a traffic descriptor declared through a subscriber terminal in case of a connection set-up request. More concretely, the present invention accurately estimates an average cell rate of data traffic for each connection in accordance with a traffic descriptor declared by a user and database information of a management system at the network side and decides whether to set up connections in accordance with the estimated result.
The present invention makes it possible to accurately obtain an average cell rate by considering the load state of a network and effectively use network resources in accordance with bandwidth allocation corresponding to the utilization condition of a network because a network-side system estimates an average cell rate of each connection. Moreover, because a user terminal does not have to declare the value of a complicated ambiguous average cell rate as a traffic descriptor in case of a connection set-up request, the declaration procedure is simplified.